As a global recommendation, the WHO guidelines recommend exclusive breastfeeding for the first 6 months with complimentary breastfeeding up to 2 years of age. Although breastfeeding carries health, economic and psychological benefits, prolonged breastfeeding has been proposed to have more cariogenic properties than cow’s milk. Prolonged breastfeeding has been reported to carry an increased risk of development dental caries in early childhood.

This cohort study, conducted in the Khon Kaen region of Thailand, aims to test the hypothesis that a longer breastfeeding duration increases the risk for dental caries in primary teeth.

Methods

The children who participated in the study were part of a wider population-based birth cohort study investigating the impact of multiple early environmental factors on a child’s general health in later life. 556 children were included in this current study.

This group included all children born in Khon Kaen between January 20, 2001, and January 20, 2002 who consented to be part of the wider cohort study and who had an oral examination at 3-4 years by a dentist. The water fluoride content of this area is <0.3ppm. All of the children in this study were breastfed to some extent.

Mothers were interviewed based on a series of structured questionnaires eight times from pre-natal to 36 months. This investigated initial social information (income, level of education, occupation) and gathered information on breastfeeding including extent of breastfeeding, bottle feeding, frequency of feeding and information on tooth-brushing and confectionery consumption.

Two calibrated dentists conducted a full-mouth examination without radiographs for dental caries in a field setting using a decayed, missing, and filled surfaces (dmfs) index when the child was between 3 and 4 years of age.

Results

Breastfeeding duration was categorised into four groups: <6, 6–11, 12–17, and ≥ 18 months. The authors selected 2 groups from the cohort for comparison: ‘Full Breastfed’ ie. those breastfed with additional drinks (excluding formula) and ‘Any Breastfed’ ie. those breastfed along with additional drinks including formula.

The results did not find any significant association between duration of breast-feeding and dental caries.

‘Prolonged’ breast-feeding was not associated with increased caries incidence.

Children who were breastfed until 6-11mths had significantly lower risk for caries than those breastfed for <6mths. (85% with caries at 3 years compared with 82% with caries at 3 years)

90% of children who were breastfed beyond 12mths (who may also have had other liquids to drink but no formula milk) had caries at 3yrs.

89% of children who were breastfed beyond 12mths (who were given other liquids to drink including formula milk) had caries at 3yrs.

9% of those breastfed to 12-18mths were reported to fall asleep while feeding >3x / week

Conclusions

The authors concluded: –

That they did not observe an association between prolonged ‘full’ or ‘any’ breastfeeding for >12 months and increased caries risk.

And

that their study suggests the benefit of full breastfeeding for 6–11 months for dental caries prevention in primary teeth.

Comments

It must be highlighted that in this study, 85% of children who stopped breast feeding by 12 months had caries at 3 years, whereas 90% of children who were breastfed up to 17mths had caries. Only 8 children were breastfed beyond 18mths and 100% of these had dental caries at 3 years. Therefore, the longer children were breastfed, the more caries that was observed at 3 years of age. This trend was not found to be significant.

This is a population of high caries risk with the average dmfs reported as being 14.2. The majority of women in the study were not educated beyond primary school, and the poorer mothers tended to breastfeed longer.

There are a number of areas where this study could have been improved and a number of confounders which were not accounted for and contribute to a high degree of bias.

Despite the author’s recording of dmfs, we are not told which sites were affected by caries. Caries due to breastfeeding is most likely to occur on upper incisors, canines and first primary molars. This information would have been valuable.

Dental examinations were carried out with natural light only (no dental light)

No information was provided on frequency of nocturnal feeding, or average length of breastfeeds. The only information given on “falling asleep while feeding” was whether the child fell asleep >3 times per week.

We are not told whether the children co-sleep with the mother and whether breastfeeding is on-demand.

We have only vague information on sugar consumption and there is no detail on what additional drinks were being given to the child, their frequency and whether given in a bottle or cup.

In this study, there was a high degree of bias due to confounding factors which were not accounted for. Although caries was not significantly found to increase with prolonged breastfeeding, caries was highly prevalent in this population which may impact on its generalisability. However, the findings are similar to a 2015 review by Tham et al (Dental Elf- 15th Nov 2015).

Derek Richards is the Director of the Centre for Evidence-based Dentistry, Editor of the Evidence-based Dentistry Journal, Consultant in Dental Public Health with Forth Valley Health Board and Honorary Senior Lecturer at Dundee & Glasgow Dental Schools. He helped to establish both the Centre for Evidence-based Dentistry and the Evidence-based Dentistry Journal. He has been involved with teaching EBD and a wide range of evidence-based initiatives both nationally and internationally since 1994.